Question

The average age of the $40$ members of a computer science camp is $17$ years. There are $20$ girls, $15$ boys, and $5$ adults. If the average age of the girls is $15$ and the average age of the boys is $16,$ what is the average age of the adults?

$26$

$27$

$28$

$29$

$30$

Solution:

The sum of the ages of everybody at the camp is $40 \cdot 17 = 680.$

The sum of the ages of the girls is $20 \cdot 15 = 300$ and of the boys is $15 \cdot 16 = 240.$

As such, we know that the ages of the adults must be $680 - 300 - 240 = 140.$

And therefore, the average age of the adults is then $140 \div 5 = 28.$

Thus, C is the correct answer.

1999 AMC 8 Problem 13

Solution:

Problem 13 in Other Years